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An integrated biomanetostratigraphic chronology for the Mediterranean Pliocene has been developed in the last five years mainly from land sections in Southern Italy (Calabria and Sicily) and ODP Leg 107 (Tyrrhenian Sea) cores. In this paper, the chronology is applied to terrigenous sediments from the Northern Apennine foredeep where reworking, as well as sedimentation rate and facies variations, limit the resolution of biostratigraphy and physical stratigraphy. The integrated chronology gives improved stratigraphic control for a Messinian to Upper Pliocene section exposed on the banks of the Stirone near Parma (Northern Italy) and for a short Lower Pliocene section located nearby at Sant'Andrea Bagni. The sections are in the vicinity of stratotype sections for the tabianian (Lower Pliocene) and Piacenzian (Upper Pliocene), and the chronology gives new insights into the complex Pliocene sedimentation history in the Northern Apennine foredeep at this time. At the Stirone section, the base of the Pliocene record is in a normal polarity chronm correlated to the Thvera subchron, indicating a hiatus at the Miocene/Pliocene boundary and the absence of the MPL1 foraminiferal zone. At Sant'Andrea Bagni, MPL1 is also missing, in contrast to previous reports. We conclude that this biozone is probably absent throughout the Northern Apennines where post-Messinian flooding appears to have occurred at the onset of MPL2 time. During the Gilbert Chron, sedimentation rates at Stirone reached 104 cm/kyr, as nearly 300 m of “argille azzurre” (blue clay) were deposited in less than 0.5 Myr. Very sporadic sedimentation is apparent from the Late Nunivak to the top of the section (late Gauss Chron), with a number of hiatuses being recognized within Chron 2Ar (late Gilbert) and in the early Gauss. This interruption of sedimentation at about 4.1 Ma is associated with a widely recognized Early Pliocene tectonic event involving thrusting and migration of the depocenter of the Northern Apennine foredeep.

A new integrated calcareous plankton biostratigraphy for the Mediterranean has been developed in the last few years which allows the continuous Plio-Pleistocene sedimentary sequence recovered at Site 653 to be rather precisely corre­ lated to other Leg 107 Sites and to sedimentary sequences on land. Although no magnetostratigraphy is available from Site 653, the biostratigraphic correlations to magnetostratigraphically controlled Mediterranean sections allow the se­ quence at Site 653 to be indirectly correlated to the geomagnetic reversal timescale. The correlation of the chronostratig­ raphy at Site 653 to the Plio-Pleistocene proposed stratotype sections indicates several anomalies in the time coverage of the stratotype sections. Hiatuses are present at the top of the Zanclean stratotype section at Capo Rossello and at the base of the Piacenzian stratotype section (in the Arda valley). In addition the Piacenzian stratotype section does not reach the Plio-Pleistocene boundary. There is therefore a gap of about 0.85 m.y. which is not covered by a stratotype section. As the top of the Piacenzian stratotype corresponds to a rather important climatic event (the onset of Northern Hemisphere Glaciation and the "Glacial Pliocene"), we advocate maintaining the Piacenzian as a chronostratigraphic unit and propose a threefold subdivision of the Pliocene. For the early Pleistocene, the previously proposed stratotype sections also do not adequately cover the time interval. For example, the Calabrian and Sicilian stratotype sections largely overlap. It has been suggested that the Calabrian stage be abandoned and that the Santernian, Emilian, and Si­ cilian be combined into a single stage, referred to as the Selinuntian.

An AGU Chapman Conference, “Time scales of the Geomagnetic Field,” was held recently on the 70th birthday of Neil D. Opdyke, professor at the University of Florida, as a tribute to his outstanding contributions to the Earth sciences over more than 4 decades. Seventy-five participants, a quarter of whom came from outside North America, registered for the meeting and took part in the scientific sessions. The meeting was organized into three topics, each of which occupied a day of lectures and posters.

[1] The deconvolution scheme of Oda and Shibuya [1996], designed for half-core data from the pass-through magnetometer aboard the Joides Resolution, has been adapted for treatment of u-channel data. The program was tested using u-channels from Ocean Drilling Program (ODP) Site 1090. A significant increase in resolution of the u-channel data can be achieved by deconvolution, resulting in data comparable with that obtained by continuous discrete sampling. Large amplitude changes of the magnetization vector revealed by the deconvolution treatment are in good agreement with the results obtained on discrete samples extracted from the same u-channels. Application of this procedure to u-channel data from ODP Sites 983 and 984, over a short time interval around 1.255 Ma, permitted enhanced definition of the so-called Bjorn geomagnetic event.

The timing of rifting and subduction in the Meliata, Vardar, and Pindos zones of the Hellenic-Dinaric-Carpathian region indicates that they cannot be considered remnants of a single ocean basin, in contrast to several recently published Mesozoic paleogeographies. Sea-floor spreading in the Meliata zone culminated in Middle Triassic (Ladinian) time and ceased in the Late Triassic, and subduction occurred from this time until Late Jurassic closure. In contrast, sea-floor spreading in the Vardar zone began in Early Jurassic time and culminated in the Middle Jurassic, and subduction occurred from latest Jurassic time. In the Pindos zone, sea-floor spreading was initiated in the Early Triassic, with Late Jurassic and early Tertiary subduction.

Transgressive-regressive cycles are recognized in early to middle Pleistocene siliciclastic shelf sediments that crop out in the tectonically active Crotone basin (southern Italy). Chronological constraints from calcareous nannofossil biostratigraphy and magnetostratigraphy indicate that these cycles are synchronous with oxygen isotope stages 19 to 33 and hence with global sea-level fluctuations. A major facies break in the succession correlates with oxygen isotope stages 22–24, corresponding to the major mid-Pleistocene climatic shift. These findings indicate that Pleistocene eustatic oscillations can be recognized in the lithostratigraphy of a tectonically active siliciclastic shelf setting. By integrating biomagnetostratigraphy with physical stratigraphy, a highly resolved chronology can be developed for these settings similar to that available for deep-sea sediments.

The quest for improved time control, to estimate rates of geologic and paleoenvironmental processes, is central to the Earth sciences. Until the middle of this century, geochronology was based solely on macrofossil evolution, providing the largely unmodified definition of geologic stages. In the last few decades, with impetus from the Deep Sea Drilling Project (DSDP) and the Ocean Drilling Program (ODP), microfossil biostratigraphy has become increasingly important. Although new radiometric techniques have resulted in improved absolute age precision, the direct correlation of absolute ages to biozonations (and hence to geologic stage boundaries) remains poor. This is due to the difficulty of finding materials suitable for radiometric dating which can be directly correlated to biozonations. The bridge between biozonations and absolute ages and the interpolation between absolute ages are best accomplished, particularly for Cenozoic and late Mesozoic time, through the geomagnetic polarity timescale (GPTS). The template for Late Jurassic to Quaternary geomagnetic polarity is derived from oceanic magnetic anomalies. As demonstrated by Heirtzler et al. [1968], the GPTS can be constructed using oceanic magnetic anomaly record(s), assuming constant seafloor spreading rate(s), and interpolating between available radiometric ages. In the last quadrennium, there have been outstanding developments in radiometric dating and astrochronology which have greatly improved the absolute age control of the GPTS.

High-resolution rock magnetic data, atomic mass spectroscopy 14 C dates, δ 18 O, and grain-size analyses from a piston core (HU90-013-013) located off southwest Greenland provide a record of the last two deglaciations. During Termination I, a welldefined interval having high volumetric magnetic susceptibility (k) and a low ratio of anhysteretic susceptibility to volumetric magnetic susceptibility ( k ARM / k ) postdates the Younger Dryas and the δ 18 O change marking the stage 2/1 boundary and correlates with sedimentological and geomorphological evidence for Greenland ice-sheet retreat from the coastline to the continental interior. During Termination II, a very similar magnetic signal coincides with the δ 18 O shift marking the stage 6/5 glacial-interglacial transition and continues throughout substage 5e. We suggest that this magnetic signal, during both Termination I and Termination II, marks continental meltwater–carried detritus from Greenland. If so, the synchronous changes in magnetic and oxygen isotopic records at Termination II indicate very early and rapid deglaciation of Greenland, in contrast to the relatively late deglaciation observed for Termination I. Distinct fluctuations in k and k ARM / k occur below the onset of the δ 18 O change at Termination I (where they occur at ∼16 900 yr B.P.) and at Termination II. These fluctuations are interpreted as due to sudden influxes of detritus into the basin caused by unpinning of ice from the continental shelf at the inception of deglaciation.

A characteristic magnetization has been isolated from 18 sites in Middle Ordovician igneous and sedimentary rocks from the Builth inlier, Wales. Two conglomerate tests demonstrate that the characteristic magnetization in two of the volcanic units was acquired early, perhaps during initial emplacement. Six sites from the northern and central parts of the inlier give a mean direction of D=153.8°, I=69.8° (k=45.8; α95=10°) that passes a regional fold test. However, 12 sites from the southern end of the inlier, in and near the Llanelwedd quarry, yield a significantly different direction after correction for local tilt: D=176.4°, I=44.5° (k=42.4; α95=6.7°). The Llanelwedd quarry data are anomalous with respect to both results from the northern parts of the inlier, and those obtained from approximately coeval rocks from the Shelve inlier. We have searched for an explanation for the discrepancy between the magnetization directions of the two areas and have now ruled out some possibilities, including superimposed magnetization components at one of the two areas. The Llanelwedd quarry lies within a wedge of dominantly andesitic volcanic rocks that appear only locally, and which are overlain by two unconformities that are also not present elsewhere in the inlier. One possible explanation for the anomalous nature of the Llanelwedd quarry magnetization is that the strata were not horizontal at the time of magnetization, either due to early volcano-tectonic tilting or primary dips on the flanks of a volcano. Another possibility is that the Llanelwedd quarry rocks were extruded rapidly enough that the geocentric coaxial dipole field hypothesis cannot be applied. Results from Cenozoic volcanic rocks from the western United States suggest that even highly anomalous fields can be preserved virtually unchanged over a number of separate flow events. We currently regard this to be the most viable explanation for the anomalous nature of the Llanelwedd quarry magnetization. We conclude that the data from the 6 northern sites represent the best estimate of the Middle Ordovician axial dipole field for the inlier.

The Northern Calcareous Alps are generally thought to have been part of the same southern Tethyan continental margin as the southern Alps during Late Jurassic and Early Cretaceous time. Contrasting Liassic paleomagnetic data from the Northern Calcareous Alps and the southern Alps can be explained by large-scale clockwise rotation during Late Cretaceous and Tertiary tectonic emplacement of the Northern Calcareous Alps onto the European continental margin. Alternatively, the data can be reconciled by postulating that the Northern Calcareous Alps did not undergo the African Mesozoic rotational history seen in the southern Alps and were separated from the southern Alps by a short-lived branch of Jurassic ocean. Facies analysis in the Karwendel-Thiersee syncline of the Northern Calcareous Alps indicates that the Jurassic basin sediments in this area were deposited in an east-west-oriented sinistral strike-slip fault system. In the southern Alps and central Austroalpine complex, coeval basin sedimentation was controlled by north-south-oriented normal faults. This contrasting basin evolution and evidence for a source of ophiolitic detritus south of the Northern Calcareous Alps argue for a short-lived ocean basin south of the Northern Calcareous Alps that was closed by Early Cretaceous time.

The Umbrian Apennines were the site of pelagic sedimentation throughout most of the Jurassic. Magnetic stratigraphy from four sections spanning many of the Jurassic stages indicates that the geomagnetic field at this time was characterized by two intervals of mixed polarity, separated by an interval of predominantly normal polarity corresponding to the Jurassic “quiet-zone” in the oceanic magnetic anomaly record. Unfortunately, ammonites are poorly preserved or absent throughout most of these sections; the duration of this “quiet-interval” cannot be well defined, although it is probably restricted to the Callovian and Oxfordian stages.

Late Cretaceous and Eocene paleomagnetic results from calcareous mudstone, limestone, and volcaniclastic rocks in southwest Puerto Rico yield a significant anticlockwise discordance in magnetization direction relative to North American reference data. Progressive thermal demagnetization has revealed stable, characteristic high blocking temperature magnetization components that display an intrasite bipolarity. The direction of this stable magnetization in tilt-corrected coordinates is consistently either northwest and down, or southeast and up. The pole position (39.4° N.Lat.; 209.6° E.Long.; dp = 9.3°; dm = 16.7°; N = 10) suggests post Eocene anticlockwise rotation of the sampling region relative to North America by 45° about a vertical axis. A rotating block domain model in which north-south compression is superimposed on WNW-ESE strike-slip faults in SW Puerto Rico can explain the inferred rotation.

Paleomagnetic results from eight sites in argillaceous metasediments from Union County, North Carolina, in the central Carolina slate belt yield a consistent high blocking temperature magnetization component. The precision of the mean declination and inclination of all site means is maximized at 50% tilt correction, and the improvement in grouping relative to 0% and 100% tilt correction is significant at the 95% confidence level. This tends to indicate that the high blocking temperature component was acquired during folding. The metamorphism and deformation in this area are rather well constrained, by recent 40Ar/39Ar data, to the Late Ordovician (−450 Ma). We therefore interpret the computed pole position (29.6°N, 122.1°E, α95 = 5.11) as Late Ordovician in age and note that it lies close to some of the Late Ordovician poles for cratonic North America. The paleolatitude (22.2°S) of the sampling site is certainly unlike those derived from Armorica and Gondwana for this time interval and is rather similar to that proposed for the Iapetus coast of Laurentia during the Late Ordovician. Indeed, the magnetization (and deformation) may be contemporaneous with the docking of the Carolina slate belt onto the Laurentian continent.

The Cretaceous-Tertiary boundary is exposed in shallow marine coastal plain sediments near Braggs, Alabama. Magnetic stratigraphy across the boundary indicates that Chron 29R is represented by a stratigraphic thickness of 2.91 (±0.48)m. The average sedimentation rate in this chron is therefore 5.1 m/m.y. The apparent macrofaunal extinction at C29.15R is significantly below the nannofossil extinction event at C29.45R. In the pelagic realm, the microfaunal extinction event is consistently found between C29.7R and C29.8R. The discordance between the microfaunal and macrofaunal extinction events at Braggs, and between the microfaunal extinctions in pelgic sections and at Braggs, may be due to local changes in sedimentary environment in the Braggs section, which culminate in an erosional uncomformity at C29.15R. The minimum estimate for the apparent time lag between the two extinction events at Braggs is about 80,000 yr. Rock magnetic experiments and the analysis of magnetic separates indicate the presence of magnetite, hematite and pyrrhotite as potential magnetic remanence carries. Two phases of magnetite one detrital titanomagnetite and one euhedral low-titanium magnetite, have been identified by electron microscopy, X-ray diffraction and electron diffraction techniques. The euhedral low-titanium magnetite is fine grained (

The carbon isotope record in four pelagic carbonate sections from the Southern Alps (northern Italy) across the Jurassic-Cretaceous boundary has been correlated to biostratigraphy and magnetostratigraphy. The carbon isotope curve from bulk carbonates shows a decrease from Kimmeridgian to Early Tithonian (CM24–CM22) values of δ13C=+2.07 (± 0.14)‰ to Late Tithonian and Berriasian (CM18–CM14) values of δ13C=+1.26 (± 0.16)‰. The change in the carbon isotope record coincides with changes in Tethyan calcite and silica accumulation rates, with a drop in the calcite compensation depth in the Atlantic and Tethys oceans and with changes in organic carbon burial along the Eurasian margin of the Tethys. Reduced surface water productivity due to diminished transfer rates of biolimiting elements into the Atlantic and Tethys oceans can explain these observations. The decreased transfer rates of elements such as silica or phosphorus from continents into the oceans resulted from drier climatic conditions and decreased water runoff on continents bordering the Tethys and Atlantic oceans. The proposed changes in Tithonian - Berriasian ocean chemistry and paleoclimate suggest that variations in the global carbon cycle were coupled with changes in the global hydrological cycle and in associated material cycles.

Leg 107 of the Ocean Drilling Program drilled a west-northwest-east-southeast transect of seven sites across the Tyrrhenian Sea, the youngest of the sub-basins of the Mediterranean Sea. Sites 654, 653, 652, and 656 document the rifting and subsidence of the Sardinia passive continental margin. On the upper margin (Site 654), we cored a classic transgressive sequence: subaerial conglomerates, overlain by oyster-bearing sands, overlain by marine marl. Comparison between the recovered lithologies and seismic reflection profiles suggests that the synrift sediments on the upper margin are Tortonian (late Miocene) to Messinian (latest Miocene) in age, whereas synrift sediments on the lower margin are Messinian to Pliocene in age. During the Messinian desiccation of the Mediterranean, Sites 654 and 653, now on the upper Sardinian margin, apparently occupied a basinal setting, where they received nannoplankton-bearing clays interbedded with laminated gypsum. Sites 656 and 652, now on the lower Sardinia margin, were apparently higher standing during the desiccation event; their Messinian facies are subaerial and lacustrine, respectively. We infer from these lines of evidence that tilting and subsidence occurred more than a million years earlier on the upper margin than on the lower margin. Such diachroneity can be interpreted in terms of migration of the zone of maximum extension above a "rolling-back" subduction zone, or in terms of extension of continental crust, by shear along a deep "detachment fault." Sites 655, 651, and 650 were drilled into two small basalt-floored basins of the central and eastern Tyrrhenian. Emplacement of basaltic crust in the central Tyrrhenian (Vavilov Basin) apparently began more than a million years before, emplacement of basaltic crust in the eastern Tyrrhenian (Marsili Basin). This observation is compatible with previous suggestions that the Tyrrhenian has grown southeastward in response to "rollback" of the down-going slab that currently dips northwestward under the toe of Italy. At the easternmost site, high vesicularity of the basalt and benthic foram assemblages in the oldest sediments imply that the basalt erupted in water shallower than 2,500 m. It has apparently subsequently subsided to its present depth of >4,100 m below sea level nearly three times as fast as normal subsidence of crust formed at a mid-ocean ridge.

Magnetite, haematite, and to a minor extent maghaemite are recognised in the Cretaceous and Paleocene red pelagic limestones at Gubbio. The magnetite is detrital (or biological), whereas the haematite grew during diagenesis from a goethitic precursor. Thermal and AF demagnetization of samples collected from close to reversal boundaries indicate that the various magnetization components do not record the polarity reversal at exactly the same stratigraphic level. In the few tens of centimetersbelow a recorded geomagnetic reversal, defined by the magnetite magnetization, some of the haematite grains are magnetized in the post-reversal field. The blocking temperature spectra of this haematite fraction (with post-reversal magnetization) are found to shift toward higher temperatures as the reversal boundary is approached. The blocking temperature spectra reflect the grain size spectra of the haematite, which we interpret as arising by the continual nucleation of grains down to a certain burial depth where the conditions are no longer conducive to further haematite growth. The depth below reversal boundaries to which haematite with post-reversal magnetization can occur, is estimated to be about 60 cm (after compaction), and is equivalent to a time of about 105 years for these particular sediments. A detailed study of the magnetization components at reversal boundaries indicates that the first diagenetic growth of haematite through the single-domain critical volume occurs prior to the mechanical fixation of the detrital (or biological) magnetite. Subsequently the diagenetic haematite grains do not rotate in response to the ambient geomagnetic field polarity as easily as the magnetite, because of their occurrence as pigmentary coatings on larger non-magnetic grains.

We have conducted a paleomagnetic study of limestones and chalks from Haiti which suggests that the island of Hispaniola is a composite of at least two tectonically independent blocks. Sampling sites are distributed among three widely separated localities, namely: Les Cayes (nine sites; 18.3°N. Latitude; 73.6°W. Longitude) and Beloc (five sites; 18.4°N. Latitude; 72.6°W. Longitude) which are located on the southern peninsula of Haiti, and a northern locality, Ennery (six sites; 19.5°N. Latitude; 72.5°W. Longitude). Stable magnetization components of dual polarity and moderately high blocking temperature were revealed through progressive thermal demagnetization of samples from all of the Beloc and Ennery sites, while seven of the nine Les Cayes sites possessed unstable magnetizations. Mean paleolatitudes calculated from Beloc and Ennery data show 8° of latitudinal separation that is of at least Eocene age. Pole positions (Beloc: 43.2°N. Latitude; 185.8°E. Longitude, α95=25.1° and Ennery: 66.1°N. Latitude; 31.3°E. Longitude, α95=19.7°) show both colatitudinal and angular discordance with the North American apparent polar wander path. Based on these disparities, we demonstrate that the implied tectonic displacements tend to support some aspects of previously published Caribbean plate tectonic models.

Knowledge of the polarity history of the Earth’s magnetic field during the Mesozoic stems primarily from oceanic (M-sequence) magnetic anomalies. Certain of these anomalies have been biostratigraphically dated from sediments immediately overlying basaltic basement at Deep Sea Drilling Project (D. S. D. P.) sites within the M-sequence. The biostratigraphic control is such that these age estimates are generally imprecise, and moreover the sediment ages represent only minimum ages for the basaltic basement itself. Magnetostratigraphy in sedimentary land sections provides improved age estimates for magnetozones, which can then be correlated with M-sequence anomalies. Magnetostratigraphy provides not only enhanced dating of the ocean floor and resolution of the behaviour of the geomagnetic field during the Cretaceous and Jurassic oceanic ‘quiet zones’, but also a world-wide correlation tool for sedimentary stratigraphy. The middle Cretaceous is characterized by a long period of normal polarity extending from the early Aptian to the early Campanian. Reversed magnetozones corresponding to oceanic anomalies M-0, M-1 and M-3 have been palaeontologically dated as early Aptian, middle Barremian and early Barremian respectively. Magnetozones corresponding to oceanic anomalies M-5 to M -15 are Hauterivian to Valanginian in age but have not been individually associated with stage boundaries, mainly due to poor biostratigraphic control in Italian pelagic limestone sections of this age. However, magnetozones corresponding to oceanic anomalies M -16 to M-22 have been individually correlated to Lower Berriasian and Tithonian palaeontological zones, and extrapolation of this correlation gives an age for anomaly M-25 close to the Oxfordian-Kimmeridgian boundary. The Jurassic 'quiet zone’ in the oceans is recognized in land sections as an extended period of predominantly normal polarity, and although poor biostratigraphic control in this interval limits our knowledge of its duration, we consider that it extended through the Oxfordian and Callovian stages. The Bathonian and older Jurassic stages are characterized by mixed polarity. A precise correspondence of magnetozones to ammonite zonations and stage boundaries is only available for the Aalenian to Pliensbachian interval, where the frequency of reversal was apparently very high.

The pre-orogenic morphology of the west Sicilian Mesozoic continental margin was characterised by platforms and basins elongated more or less parallel to the ancient junction between ocean and continent. The deformation of this continental margin during the Miocene gave rise to a number of thrust sheets which were transported southwards where they rest against the stable Iblean plateau. Eight thrust sheets have been sampled for palaeomagnetism in order to establish the amount of rotation, relative to Iblei, which occurred during emplacement. Clockwise rotations of large magnitude appear to have taken place, and these rotations are considered to be related to the emplacement of the Calabrian—Peloritani structure onto this continental margin.

Detailed records of palaeomagnetic directions from two Upper Cretaceous Umbrian sections are compared with the composite section compiled by Van den Berg et al. [1]. In addition to these sections, fifty-one geographically distributed sites have been studied magnetically and palaeontologically. The Late Miocene-Pliocene fold belt of the Umbrian Apennines is arcuate in outcrop, being convex toward the east. The fold axes are generally tangential to the Umbrian arc, which can be divided into a northern northwestern-trending part and a southern northeastern-trending part. Sites from the north have more westerly declinations than those from the south. The differences are significant at the 95% probability level and most probably reflect the bending of originally straight fold axes or the development of fold axes with initial curvature. The palaeomagnetic directions from Umbria provide important information concerning the Umbrian tectonic deformation, but are not applicable to the Italian autochthon.

Pelagic carbonate rocks possess many suitable characteristics for paleomagnetic and magnetostratigraphic studies. Paleomagnetic results are summarized for seven lengthy sections of pelagic limestones and marls from Umbria and the southern Alps in Italy. Differences in apparent polar wander paths from these two regions are interpreted in terms of tectonic rotation of allochthonous Umbria. The magnetic stratigraphies of the paleontologically dated sections are independent of their tectonic differences and are combined to form a continuous record of geomagnetic polarity for the Barremian through Maastrichtian stages of the Cretaceous. All but one of the reversals in these sections are confirmed by duplication in at least one other section. Additional Cretaceous reversals have been reported in other land sections and in DSDP (Deep Sea Drilling Project) and IPOD (International Program of Ocean Drilling) cores. Some of these reversals are not defined well magnetically, and confirmation of others is clouded by imprecise paleontological dates. If real, they are probably of short duration. The confirmed reversal sequence correlates well with the Cretaceous oceanic magnetic anomaly sequence. The ages of certain key anomalies are altered: Late Cretaceous anomalies 29–34 are younger, and Early Cretaceous anomalies M0 and M1 are older than previously thought. The longer duration of the Cretaceous magnetic quiet interval of normal polarity results in a reduction of corresponding sea floor spreading rates to about 70% of earlier values, but they are still appreciably higher than during formation of the preceding M sequence anomalies.

A composite North Atlantic record from DSDP Site 609 and IODP Site U1308 spans the past 300,000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations. Hematite-stained grains exhibit similar repetitive down-core variations within the Marine Isotope Stage (MIS) 8 and 4-2 intervals, but little cyclic variability within the MIS 6 section. There is also no petrologic evidence, in terms of detrital carbonate-rich (Heinrich) layers, for surging of the Laurentide Ice Sheet through the Hudson Strait during MIS 6. Rather, very high background concentration of iceberg-rafted debris (IRD) indicates near continuous glacial meltwater input that likely increased thermohaline disruption sensitivity to relatively weak forcing events, such as expanded sea ice over deepwater formation sites. Altered (sub)tropical precipitation patterns and Antarctic warming during high orbital precession and low 65 degrees N summer insolation appear related to high abundance of Icelandic glass shards and southward sea ice expansion. Differing European and North American ice sheet configurations, perhaps aided by larger variations in eccentricity leading to cooler summers, may have contributed to the relative stability of the Laurentide Ice Sheet in the Hudson Strait region during MIS 6.

Episodes of ice-sheet disintegration and meltwater release over glacial–interglacial cycles are recorded by discrete layers of detrital sediment in the Labrador Sea1, 2. The most prominent layers reflect the release of iceberg armadas associated with cold Heinrich events3, but the detrital sediment carried by glacial outburst floods from the melting Laurentide Ice Sheet is also preserved4. Here we report an extensive layer of red detrital material in the Labrador Sea that was deposited during the early last interglacial period. We trace the layer through sediment cores collected along the Labrador and Greenland margins of the Labrador Sea. Biomarker data, Ca/Sr ratios and δ18O measurements link the carbonate contained in the red layer to the Palaeozoic bedrock of the Hudson Bay. We conclude that the debris was carried to the Labrador Sea during a glacial outburst flood through the Hudson Strait, analogous to the final Lake Agassiz outburst flood about 8,400 years ago, probably around the time of a last interglacial cold event in the North Atlantic5. We suggest that outburst floods associated with the final collapse of the Laurentide Ice Sheet may have been pervasive features during the early stages of Late Quaternary interglacial periods.

© 2015 Elsevier Ltd. Integrated Ocean Drilling Program (IODP) Site U1308 (49°53'N, 24°14'W; water depth 3871 m) provides a record of relative paleointensity (RPI) and benthic stable isotope stratigraphy back to 3.2 Ma. The record since 1.5 Ma was published previously, and here we present the interval from 1.5 Ma to 3.2 Ma (Early Pleistocene-Late Pliocene). The benthic oxygen isotope record in this interval is correlated to Marine Isotope Stage (MIS) 51 to KM2, with an apparent hiatus that removed part of the interval spanning MIS 104-G2 (2.6-2.65 Ma), at the Gauss-Matuyama boundary. The mean sedimentation rate for the 1.5-3.2 Ma period is 8.5 cm/kyr. The age model was built by correlation of the benthic oxygen isotope record to a global stack (LR04). Apart from the expected polarity reversals, three magnetic excursions are recorded: Punaruu in MIS 31/32 at 1092 ka, Gilsa in MIS 54/55 at 1584 ka, and a newly recognized excursion labeled Porcupine (after the nearby Porcupine Abyssal Plain) in MIS G6/G7 at 2737 ka. The ages of polarity reversals at Site U1308, on the LR04 time scale, are consistent with the current geomagnetic polarity timescale (GPTS) with the exception of the base of the Olduvai Subchron that occurred in MIS 73, corresponding to 1925 ka on the LR04 time scale, 25 kyr younger than in the current GPTS. The RPI record at Site U1308 is calibrated using the oxygen isotope age model, and combined with four other North Atlantic records to obtain a North Atlantic RPI stack for 1.2-2.2 Ma (NARPI-2200) that is compared with published RPI stacks: Epapis, Sint-2000 and PADM2M. For 2.2-3.2 Ma, the Site U1308 RPI record is compared with a RPI record from North Atlantic IODP Site U1314, and with the Pacific Epapis stack. The mean sedimentation rates of the North Atlantic sites in NARPI-2200 are greater (by about an order of magnitude) than most of the records incorporated in other stacks. The comparison of Epapis and NARPI-2200 yields an apparent lag for NARPI-2200 relative to Epapis, attributed the Epapis age model constructed by correlation of magnetic concentration parameters (a proxy for carbonate percentage) to a calibrated oxygen isotope record. The long RPI record from Site U1308 yields a very similar mean value for the Brunhes and Matuyama virtual axial dipole moments (7.05 × 1022 Am2), implying no polarity bias in the strength of the main geomagnetic dipole, in contrast to interpretations from Sint-2000 and PADM2M. The results strengthen the case that RPI can be used to improve global stratigraphic correlation for sites with mean sedimentation rates up to several decimeters/kyr.

The rock and paleomagnetism of shallow water Mesozoic limestones from the Helvetic nappes, the autochthonous cover sediments of the Aiguilles Rouges and Aar massifs, and the Chaine Subalpine of Switzerland and NE France have been studied. Fold tests indicate that the magnetization after alternating field (af) and thermal cleaning postdates Neogene folding; no reversed directions were observed. Acquisition of viscous remanent magnetization (VRM) in the laboratory shows that the natural remanent magnetization (NRM) intensity can be accounted for by viscous build-up during the Brunhes epoch. The alternating magnetic field required to destroy the VRM produced in various times (t) is proportional to log t. The behavior of the magnetization at low temperatures indicates that the VRM is probably held by very fine grains whose room temperature state is close to superparamagnetism. The blocking temperatures of the NRM are mainly below 350°C. Thermomagnetic experiments, coercivity spectra, rotational hysteresis, and optical examination suggest that pyrrhotite, occurring as minute inclusions within pyrite grains, is responsible for the VRM.

The magnetic stratigraphy of a 110-m section of the Early Cretaceous Maiolica pelagic limestone in the Bosso valley (Umbria, Italy) shows clearly defined magnetozones that are correlated with the geomagnetic polarity record derived from the M-sequence marine magnetic anomalies M19 to M14, and possibly M13. Using an established paleontological zonation of this section based on calpionellids, the position of the Jurassic-Cretaceous boundary is located close to the base of the negative magnetozone corresponding to anomaly M17.

A magnetostratigraphic study at Capo Spartivento (Calabria, southern Italy) indicates that the Miocene/Pliocene boundary lies in the lowest reversed interval (Chron 3r) of the Gilbert Chron. The magnetostratigraphic time frame gives an estimate close to 19 ka for the duration of individual limestone-marl couplets that characterize the lithology. The eight couplets within Chron 3r indicate that the age of the Miocene/Pliocene boundary is about 154 ka older than the age of the reversal at the top of Chron 3r (4.78 Ma). We therefore estimate the age of this boundary as 4.93 Ma, which is 420 ka younger than that given by Berggren et al. and 100 ka older than that given by Zijderveld et al. The first-appearance datums of Globorotalia margaritae and Globorotalia puncticulata are similarly estimated to have ages of 4.66 and 4.15 Ma, respectively, the former being considerably younger than its first appearance in the open ocean.

Paleomagnetism is a quantitative tool for determining relative displacements and rotations of rock bodies in the geological past. During the last 20 years, paleomagnetic work in continental cratons has contributed greatly to our understanding of continental drift, but more recently, paleomagnetism has begun to be used on a more local scale, to elucidate tectonic problems in mountain belts. We have selected several geographical areas which illustrate an approach to paleomagnetism in mountain belts.

Exposed near Braggs, Alabama, is one of the few well-studied, nearly continuous shallow-marine Cretaceous/Tertiary boundary sections; it allows a glimpse of the biotic and environmental changes that occurred in the latest Cretaceous to earliest Paleocene. Paleomagnetic, strontium isotopic, and biostratigraphic data closely constrain the age of a series of lithologic, geochemical, and biotic variations and suggest that no more than 100–200 ka could be missing at the boundary. A major reduction in macrofaunal diversity associated with lithofacies changes occurs prior to but within 300 ka of the nannofossil-defined boundary. Approximately 40% of the apparent faunal reduction is attributed to the “Lazarus effect.” Faunal and floral assemblages, trends in carbon isotopic composition of benthic invertebrates, and lithologic characteristics indicate that a latest Maestrichtian regression culminated near the boundary (Chron C29R; Micula murus zone), significantly later than recent estimates. Water depths at this site remained shallow during the subsequent early Paleocene (zone NP1) transgression and did not reach depths equivalent to those of the late Maestrichtian until zone NP2. Relatively minor climatic changes across the boundary are suggested by a ≤4 °C cooling trend seen in the oxygen-isotope paleotemperatures. A high-resolution 87 Sr/ 86 Sr record from well-preserved macrofossil calcite shows a pattern of smooth variation and elevated values near the boundary; however, the early Paleocene “spike” of other workers was not found.